L-cysteine suppresses ghrelin and reduces appetite in rodents and humans.

BACKGROUND: High-protein diets promote weight loss and subsequent weight maintenance, but are difficult to adhere to. The mechanisms by which protein exerts these effects remain unclear. However, the amino acids produced by protein digestion may have a role in driving protein-induced satiety. METHODS: We tested the effects of a range of amino acids on food intake in rodents and identified l-cysteine as the most anorexigenic. Using rodents we further studied the effect of l-cysteine on food intake, behaviour and energy expenditure. We proceeded to investigate its effect on neuronal activation in the hypothalamus and brainstem before investigating its effect on gastric emptying and gut hormone release. The effect of l-cysteine on appetite scores and gut hormone release was then investigated in humans. RESULTS: l-Cysteine dose-dependently decreased food intake in both rats and mice following oral gavage and intraperitoneal administration. This effect did not appear to be secondary to behavioural or aversive side effects. l-Cysteine increased neuronal activation in the area postrema and delayed gastric emptying. It suppressed plasma acyl ghrelin levels and did not reduce food intake in transgenic ghrelin-overexpressing mice. Repeated l-cysteine administration decreased food intake in rats and obese mice. l-Cysteine reduced hunger and plasma acyl ghrelin levels in humans. CONCLUSIONS: Further work is required to determine the chronic effect of l-cysteine in rodents and humans on appetite and body weight, and whether l-cysteine contributes towards protein-induced satiety.

Central and peripheral administration of human relaxin-2 to adult male rats inhibits food intake.

AIM: Relaxin is a polypeptide hormone involved in pregnancy and lactation. It is mainly secreted by the corpus luteum and placenta, but is expressed in a number of other tissues, including heart and brain. Within the brain, relaxin is expressed in the olfactory and limbic systems, the cortex and the hypothalamic arcuate nucleus (ARC). Its cognate receptor, relaxin family peptide receptor 1 (RXFP1), is also widely expressed in the brain, including the hypothalamic ARC and paraventricular nucleus (PVN), areas important in appetite regulation. The aim of this study was to investigate whether relaxin influences food intake through central hypothalamic circuits. METHODS: The human form of relaxin, human relaxin-2 (H2) was administered centrally and peripherally to male Wistar rats and food intake measured. Behaviour was also assessed. RESULTS: Intracerebroventricular (ICV) administration of H2 significantly decreased 1-h food intake in the early dark phase [2.95 ± 0.45 g (saline) vs. 0.95 ± 0.18 g (180 pmol H2), p < 0.001]. ICV administration of H2 decreased feeding behaviour and increased grooming and headdown behaviour. Intraparaventricular injections of H2 significantly decreased 1-h food intake in the early dark phase [3.13 ± 0.35 g (saline) vs. 1.35 ± 0.33 g (18 pmol H2), p < 0.01, 1.61 ± 0.31 g (180 pmol H2), p < 0.05 and 1.23 ± 0.32 g (540 pmol H2), p < 0.001]. Intraperitoneal (IP) administration of H2 significantly decreased 1-h food intake in the early dark phase [4.63 ± 0.46 g (vehicle) vs. 3.08 ± 0.15 g (66 nmol H2), p < 0.01, 3.00 ± 0.17 g (200 nmol H2), p < 0.01 and 2.26 ± 0.36 g (660 nmol H2), p < 0.001]. CONCLUSIONS: Central and peripheral administration of H2 reduces the food intake in rats. This effect may be mediated via the PVN and/or other brain regions.

Cerebellin1 is a novel orexigenic peptide.

AIM: Cerebellin1 (Cbln1) is highly expressed in the hypothalamus, a region of the brain involved in appetite regulation. However, the effects of Cbn1 on food intake are not known. The present study aimed to investigate the effect of Cbln1 on appetite regulation in rats. METHODS: We determined the effect of (i) intracerebroventricular (ICV) injection of Cbln1 on food intake, behaviour and plasma pituitary hormone levels in male Wistar rats; (ii) Cbln1 on the release of hypothalamic neuropeptides known to modulate food intake from hypothalamic explants and (iii) fasting on hypothalamic Cbln1 mRNA expression. RESULTS: (i) ICV administration of Cbln1 significantly increased food intake in rats and caused no adverse behaviours. ICV administration of Cbln1 significantly reduced plasma thyroid stimulating hormone (TSH) levels 10 min postinjection in rats. (ii) Cbln1 significantly increased the release of neuropeptide Y (NPY) from hypothalamic explants. (iii) Cbln1 mRNA expression levels were increased in the ventromedial nucleus of the hypothalamus in fasted rats. CONCLUSIONS: These data suggest that Cbln1 is a novel orexigenic peptide, which may mediate its effects via hypothalamic NPY.

The thyroid hormone derivative 3-iodothyronamine increases food intake in rodents.

BACKGROUND: The thyroid hormone derivative 3-iodothyronamine (T(1)AM), an endogenous biogenic amine, is a potent agonist of the G protein-coupled trace amine-associated receptor 1 (TAAR1). T(1)AM is present in rat brain, and TAAR1 is expressed in hypothalamic nuclei associated with the regulation of energy homeostasis. AIM: The aim of this study was to determine the effects of T(1)AM on food intake in rodents. METHODS: We determined the effect of (i) intraperitoneal (i.p.) administration of T(1)AM on food intake, oxygen consumption (VO(2)) and locomotor activity in mice; (ii) intracerebroventricular (ICV) injection of T(1)AM on food intake in male rats; (iii) c-fos expression following ventricular administration of T(1)AM in male rats; and (iv) direct injection of T(1)AM into the arcuate nucleus (ARC) of male rats on food intake. RESULTS: (i) T(1)AM (4 nmol/kg) significantly increased food intake following i.p. injection in mice but had no effect on VO(2) or locomotor activity. (ii) ICV administration of T(1)AM (1.2 nmol/kg) significantly increased food intake in male rats. (iii) Intraventricular administration of T(1)AM significantly increased c-fos expression in the ARC of male rats. (iv) Direct administration of T(1)AM (0.12, 0.4 and 1.2 nmol/kg) into the ARC of male rats significantly increased food intake. CONCLUSION: These data suggest that T(1)AM is an orexigenic factor that may act through the ARC to increase food intake in rodents.

Co-administration of SR141716 with peptide YY3-36 or oxyntomodulin has additive effects on food intake in mice.

BACKGROUND: SR141716 has been shown to significantly inhibit food intake and reduce body weight by antagonizing CB(1) receptors. The gut hormones peptide YY(3-36) (PYY(3-36)) and oxyntomodulin (OXM) inhibit food intake through Y(2) and Glucagon-Like-Peptide (GLP)-1 receptors respectively. OBJECTIVE: To determine the effects of co-administration of SR141716 with either PYY(3-36) or OXM in mice on food intake. METHODS: Mice (n = 14 per group) were fasted for 16 h prior to study days and given two intraperitoneal injections: study 1, vehicle-saline, SR141716-saline, vehicle-PYY3-36 or SR141716-PYY3-36; study 2: vehicle-saline, SR141716-saline, vehicle-OXM or SR141716-OXM. Food was returned and measured following injections. RESULTS: Co-administration of SR141716-PYY(3-36) or SR141716-OXM showed greater inhibition in food intake when compared with administration of SR141716, PYY(3-36) or OXM alone. CONCLUSION: Our data show that SR141716 in combination with PYY(3-36) or OXM reduces food intake additively in mice.

Leptin rapidly suppresses insulin release from insulinoma cells, rat and human islets and, in vivo, in mice.

Obesity is associated with diabetes, and leptin is known to be elevated in obesity. To investigate whether leptin has a direct effect on insulin secretion, isolated rat and human islets and cultured insulinoma cells were studied. In all cases, mouse leptin inhibited insulin secretion at concentrations within the plasma range reported in humans. Insulin mRNA expression was also suppressed in the cultured cells and rat islets. The long form of the leptin receptor (OB-Rb) mRNA was present in the islets and insulinoma cell lines. To determine the significance of these findings in vivo, normal fed mice were injected with two doses of leptin. A significant decrease in plasma insulin and associated rise in glucose concentration were observed. Fasted normal and leptin receptor-deficient db/db mice showed no response to leptin. A dose of leptin, which mimicked that found in normal mice, was administered to leptin-deficient, hyperinsulinemic ob/ob mice. This caused a marked lowering of plasma insulin concentration and a doubling of plasma glucose. Thus, leptin has a powerful acute inhibitory effect on insulin secretion. These results suggest that the action of leptin may be one mechanism by which excess adipose tissue could acutely impair carbohydrate metabolism.

Ghrelin stimulates insulin-induced glucose uptake in adipocytes.

The gastric and hypothalamic hormone ghrelin is the endogenous agonist of the growth hormone secretagogue receptor GHS-R1(a). Ghrelin stimulates growth hormone release and appetite via the hypothalamus. However, putative direct peripheral effects of ghrelin remain poorly understood. Rat adipose tissue expresses GHS-R1(a) mRNA, suggesting ghrelin may directly influence adipocyte function. We have investigated the effects of ghrelin on insulin-stimulated glucose uptake in isolated white adipocytes in vitro. RT-PCR confirmed the expression of GHS-R1(a) mRNA in epididymal adipose tissue. However, GHS-R1(a) expression was not detected in the peri-renal fat pads. Ghrelin increased insulin-stimulated deoxyglucose uptake in isolated white adipocytes extracted from the epididymal fat pads of male Wistar rats. Ghrelin 1000 nM significantly increased deoxyglucose uptake by 55% in the presence of 0.1 nM insulin. However, ghrelin administration in the absence of insulin had no effect on adipocyte deoxyglucose uptake, suggesting that ghrelin acts synergistically with insulin. Des-acyl ghrelin, a major circulating non-octanylated form of ghrelin, had no effect on insulin-stimulated glucose uptake. Furthermore, acylated ghrelin had no effect on deoxyglucose uptake in adipocytes from peri-renal fat pads suggesting that ghrelin may influence glucose uptake via the GHS-R1(a). Ghrelin therefore appears to directly potentiate adipocyte insulin-stimulated glucose uptake in selective adipocyte populations. Ghrelin may play a role in adipocyte regulation of glucose homeostasis.

Effects of acute and chronic relaxin-3 on food intake and energy expenditure in rats.

The effects of acute and repeated intraparaventricular (iPVN) administration of human relaxin-3 (H3) were examined on food intake, energy expenditure, and the hypothalamo-pituitary thyroid axis in male Wistar rats. An acute high dose iPVN injection of H3 significantly increased food intake 1 h post-administration [0.4+/-0.1 g (vehicle) vs 1.6+/-0.5 g (180 pmol H3), 2.4+/-0.5 g (540 pmol H3) and 2.2+/-0.5 g (1,620 pmol H3), p<0.05 for all doses vs vehicle]. Repeated iPVN H3 injection (180 pmol/twice a day for 7 days) significantly increased cumulative food intake in ad libitum fed animals compared with vehicle [211.8+/-7.1 g (vehicle) vs 261.6+/-6.7 g (ad libitum fed H3), p<0.05]. Plasma leptin was increased in the H3 ad libitum fed group. Plasma thyroid stimulating hormone was significantly decreased after acute and repeated administration of H3. These data suggest H3 may play a role in long-term control of food intake.

Central relaxin-3 administration causes hyperphagia in male Wistar rats.

Relaxin-3 (INSL-7) is a recently discovered member of the insulin superfamily. Relaxin-3 mRNA is expressed in the nucleus incertus of the brainstem, which has projections to the hypothalamus. Relaxin-3 binds with high affinity to the LGR7 receptor and to the previously orphan G protein-coupled receptor GPCR135. GPCR135 mRNA is expressed predominantly in the central nervous system, particularly in the paraventricular nucleus (PVN). The presence of relaxin-3 and these receptors in the PVN led us to investigate the effect of central administration of relaxin-3 on food intake in male Wistar rats. The receptor involved in mediating these effects was also investigated. Intracerebroventricular injections of human relaxin-3 (H3) to satiated rats significantly increased food intake 1 h post administration in the early light phase [0.96 +/- 0.16 g (vehicle) vs. 1.81 +/- 0.21 g (180 pmol H3), P < 0.05] and the early dark phase [2.95 +/- 0.45 g (vehicle) vs. 4.39 +/- 0.39 g (180 pmol H3), P < 0.05]. Intra-PVN H3 administration significantly increased 1-h food intake in satiated rats in the early light phase [0.34 +/- 0.16 g (vehicle) vs. 1.23 +/- 0.30 g (18 pmol H3), P < 0.05] and the early dark phase [4.43 +/- 0.32 g (vehicle) vs. 6.57 +/- 0.42 g (18 pmol H3), P < 0.05]. Feeding behavior increased after intra-PVN H3. Equimolar doses of human relaxin-2, which binds the LGR7 receptor but not GPCR135, did not increase feeding. Hypothalamic neuropeptide Y, proopiomelanocortin, or agouti-related peptide mRNA expression did not change after acute intracerebroventricular H3. These results suggest a novel role for relaxin-3 in appetite regulation.

Implantation of fibre encapsulated RIN 1056a cells transfected with NPY cDNA into the lateral ventricle of rats alters body weight.

Neuropeptide Y (NPY) is a hypothalamic neuropeptide thought to play an important role in the regulation of food intake and energy expenditure. Our aim was to over-express bioactive NPY in the lateral ventricle by implanting cells transfected with NPY cDNA. Cells from the RIN 1056a clonal rat islet cell line were transfected with NPY cDNA. Radioimmunoassay, chromatography and receptor binding assays were used to ensure the secreted NPY was bioactive, before and after implantation. NPY cDNA transfected and untransfected control cells were encapsulated in PVDF hollow fibres to prevent tumour formation and implanted into the lateral ventricle of male Wistar rats. The effects on body weight and food intake were measured for 15 days. Animals implanted with NPY cDNA transfected RIN 1056a cells showed a greater rise in body weight than controls. This difference was statistically significant five days after implantation, and remained so until the end of the experiment. Cumulative food intake was also increased in rats implanted with NPY cDNA transfected RIN 1056a cells, but this difference failed to reach statistical significance. We have demonstrated that implantation of NPY over-expressing cells into the lateral hypothalamus of rats increases body weight gain.

Agouti related protein (AgRP) is upregulated in Cushing's syndrome.

Alpha melanocyte-stimulating hormone (alpha-MSH) is an agonist at the melanocortin 3 (MC3-R) and melanocortin 4 (MC4-R) receptors. Alpha-MSH stimulates corticosterone release from rat and human adrenal cells. Patients with Cushing's syndrome have elevated levels of serum alpha-MSH. Agouti related protein (AgRP) is an endogenous antagonist at the MC3-R and MC4-R and is expressed in the rat adrenal cortex. AgRP antagonises alpha-MSH-induced corticosterone release from rat and bovine adrenal cells. This suggests that AgRP may have an inhibitory paracrine role in the adrenal gland. We measured adrenal AgRP mRNA expression and circulating AgRP in 2 patients with Cushing's syndrome and controls. Adrenal AgRP mRNA expression and plasma AgRP were higher in the patients with Cushing's syndrome compared to controls. Plasma AgRP in the patients with Cushing's syndrome following bilateral adrenalectomy and hydrocortisone replacement were similar to the levels seen in controls. Our results suggest that AgRP may have a novel inhibitory paracrine role in the human adrenal gland.

Relative Importance of the Arcuate and Anteroventral Periventricular Kisspeptin Neurons in Control of Puberty and Reproductive Function in Female Rats.

Kisspeptin plays a critical role in pubertal timing and reproductive function. In rodents, kisspeptin perikarya within the hypothalamic arcuate (ARC) and anteroventral periventricular (AVPV) nuclei are thought to be involved in LH pulse and surge generation, respectively. Using bilateral microinjections of recombinant adeno-associated virus encoding kisspeptin antisense into the ARC or AVPV of female rats at postnatal day 10, we investigated the relative importance of these two kisspeptin populations in the control of pubertal timing, estrous cyclicity, and LH surge and pulse generation. A 37% knockdown of kisspeptin in the AVPV resulted in a significant delay in vaginal opening and first vaginal estrous, abnormal estrous cyclicity, and reduction in the occurrence of spontaneous LH surges, although these retained normal amplitude. This AVPV knockdown had no effect on LH pulse frequency, measured after ovariectomy. A 32% reduction of kisspeptin in the ARC had no effect on the onset of puberty but resulted in abnormal estrous cyclicity and decreased LH pulse frequency. Additionally, the knockdown of kisspeptin in the ARC decreased the amplitude but not the incidence of LH surges. These results might suggest that the role of AVPV kisspeptin in the control of pubertal timing is particularly sensitive to perturbation. In accordance with our previous studies, ARC kisspeptin signaling was critical for normal pulsatile LH secretion in female rats. Despite the widely reported role of AVPV kisspeptin neurons in LH surge generation, this study suggests that both AVPV and ARC populations are essential for normal LH surges and estrous cyclicity.

Cloning and molecular characterization of complementary deoxyribonucleic acid corresponding to a novel form of pituitary adenylate cyclase-activating polypeptide messenger ribonucleic acid in the rat testis.

Pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide that greatly stimulates adenylyl cyclase activity in cultured anterior pituitary cells, was isolated from ovine hypothalamus in 1989. Investigation of the distribution of PACAP messenger RNA (mRNA) in rat tissues by Northern blot analysis revealed an anomalous signal in the testis. In this study we have isolated and characterized this unusual mRNA, which is approximately 800 bases long (approximately 1.5 kilobases shorter than that reported in the rat hypothalamus). Cloning and sequencing of the complementary DNA corresponding to this message revealed that the sequences are identical except for 126 bases at the 5'-end of the 5'-untranslated region of the smaller transcript. This region has no homology to either the published hypothalamic sequence or any other known sequence. Northern blot analysis of total RNA from various species showed that a smaller form of PACAP mRNA is also present in human, murine, and bovine testis, although in these species the message is slightly smaller. In addition, Northern blot analysis of these tissues using a probe directed to the 126-base 5'-region, revealed conservation of this sequence between species. Although the structure of the rat PACAP gene is unknown, preliminary investigations into the origins of the two mRNA species by PCR of genomic DNA suggests that they are transcribed from separate genes and not the product of alternate splicing.

gamma-MSH increases intracellular cAMP accumulation and GnRH release in vitro and LH release in vivo.

The roles of the melanocortin 3 receptor (MC3-R) and its agonist, gamma(2)-melanocyte-stimulating hormone (gamma(2)-MSH) in the regulation of the hypothalamo-pituitary-gonadal (HPG) axis are poorly understood. Here we show gamma(2)-MSH stimulated intracellular cAMP accumulation and gonadotrophin-releasing hormone (GnRH) secretion in the immortalised GnRH cell line GT(1)-7. The MC3/4-R antagonist Agrp blocked these actions. Reverse transcriptase polymerase chain reaction demonstrated GT(1)-7 cells express MC3-R mRNA. gamma(2)-MSH also stimulated GnRH release from hypothalamic explants. In vivo, gamma(2)-MSH administration into the medial preoptic area significantly increased plasma luteinising hormone. MC3-R and gamma(2)-MSH may modulate the HPG axis.

Characterization and distribution of prolactin releasing peptide (PrRP) binding sites in the rat--evidence for a novel binding site subtype in cardiac and skeletal muscle.

Prolactin releasing peptide (PrRP) was recently purified from bovine hypothalamus and binds to the orphan receptor, UHR-1. We examined the distribution and kinetics of (125)I-PrRP binding in rat tissues together with molecular characterization by chemical cross-linking and Northern blotting. In this study (125)I-PrRP binding showed specificity and rapid association and dissociation. Specific binding was found in membranes from rat tissues including brain (hypothalamus, medulla oblongata and cerebellum), pituitary, heart, soleus muscle, adipose tissue, kidney, adrenal gland, testis and small intestine. In hypothalamus, pituitary, heart and soleus competition analysis indicated only one class of binding site in each tissue. Binding affinity for PrRP (IC(50)) and binding site density (B(max)) respectively were 5.2+/-0.9 nM and 674+/-97 fmol mg protein(-1) in hypothalamus (n = 5), 1.4+/-0.6 nM and 541+/-126 fmol mg protein(-1) in pituitary (n = 3), 6.6+/-0.7 nM and 628+/-74 fmol mg protein(-1) in heart (n = 4) and 9.8+/-0.9 nM and 677+/-121 fmol mg protein(-1) in soleus muscle (n = 4). Analysis of (125)I-PrRP-binding site complexes by chemical cross-linking showed a binding site M(r) of 69,000 in hypothalamus and 41,000 in heart and soleus. Northern analysis of polyA(+) RNA from hypothalamus showed a 4.2 kb band as expected for UHR-1, but heart and soleus showed a 4.8 kb band. Taken together these results indicate that there may be different subtypes of PrRP binding sites in rat tissues which may differ from UHR-1.

Quantification and synthesis of cocaine- and amphetamine-regulated transcript peptide (79-102)-like immunoreactivity and mRNA in rat tissues.

The distribution of cocaine- and amphetamine-regulated transcript peptide (79-102)-like immunoreactivity (CART-LI) was quantified in brain and peripheral tissues of male and female Wistar rats, and male obese (fa/fa) and heterozygous (Fa/+) Zucker rats using a specific RIA. CART-LI tissue levels have not been quantified previously. The assay, using cocaine- and amphetamine-regulated transcript (CART) (79-102) as a standard and radioactive tracer and an antibody to CART (79-102) fragment, detected CART-LI in all brain regions examined, the anterior and posterior pituitary, the spinal cord and throughout the gastrointestinal tract of both male and female Wistar rats. The highest concentrations were found in the hypothalamus, duodenum, anterior pituitary and posterior pituitary (50.6+/-4.4, 26.1+/-4.2, 50.0+/-1.3 and 373.0+/-55.2 pmol/g wet tissue respectively, means+/- s.e.m., n=6-10 male animals). There was no significant variation between the sexes. The concentrations of CART-LI in hypothalami and anterior and posterior pituitaries from fa/fa rats were significantly (P<0002) lower than those of Fa/+ controls (35.9+/-2.1 vs 53.9+/-4.9,<0.6 vs 1.8+/-0.4 and 114+/-9.1 vs 255.5+/- 20.9 pmol/g wet tissue respectively, means+/- s.e.m., n=7). Gel permeation chromatography of regions of rat brain and gastrointestinal tract showed possible differential processing between regions. CART-LI was released from hypothalamic tissue slices in a calcium-dependent fashion by potassium-induced depolarisation. Northern blot analysis detected CART mRNA in the hypothalamus, anterior pituitary, brain stem, cerebellum and spinal cord. The pattern o! f distribution of CART mRNA and CART-LI in various neural and other tissues is in accord with a role for CART as a neurotransmitter.

Relaxin-3 stimulates the neuro-endocrine stress axis via corticotrophin-releasing hormone.

Relaxin-3 is a member of the insulin superfamily. It is expressed in the nucleus incertus of the brainstem, which has projections to the hypothalamus. Relaxin-3 binds with high affinity to RXFP1 and RXFP3. RXFP3 is expressed within the hypothalamic paraventricular nucleus (PVN), an area central to the stress response. The physiological function of relaxin-3 is unknown but previous work suggests a role in appetite control, stimulation of the hypothalamic-pituitary-gonadal axis and stress. Central administration of relaxin-3 induces c-fos expression in the PVN and increases plasma ACTH levels in rats. The aim of this study was to investigate the effect of central administration of human relaxin-3 (H3) on the hypothalamic-pituitary-adrenal (HPA) axis in male rodents in vivo and in vitro. Intracerebroventricular (i.c.v) administration of H3 (5 nmol) significantly increased plasma corticosterone at 30 min following injection compared with vehicle. Intra-PVN administration of H3 (1.8-1620 pmol) significantly increased plasma ACTH at 1620 pmol H3 and corticosterone at 180-1620 pmol H3 at 30 min following injection compared with vehicle. The stress hormone prolactin was also significantly raised at 15 min post-injection compared with vehicle. Treatment of hypothalamic explants with H3 (10-1000 nM) stimulated the release of corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), but H3 had no effect on the release of ACTH from in vitro pituitary fragments. These results suggest that relaxin-3 may regulate the HPA axis, via hypothalamic CRH and AVP neurons. Relaxin-3 may act as a central signal linking nutritional status, reproductive function and stress.

The physiological role of arcuate kisspeptin neurons in the control of reproductive function in female rats.

Kisspeptin plays a pivotal role in pubertal onset and reproductive function. In rodents, kisspeptin perikarya are located in 2 major populations: the anteroventral periventricular nucleus and the hypothalamic arcuate nucleus (ARC). These nuclei are believed to play functionally distinct roles in the control of reproduction. The anteroventral periventricular nucleus population is thought to be critical in the generation of the LH surge. However, the physiological role played by the ARC kisspeptin neurons remains to be fully elucidated. We used bilateral stereotactic injection of recombinant adeno-associated virus encoding kisspeptin antisense into the ARC of adult female rats to investigate the physiological role of kisspeptin neurons in this nucleus. Female rats with kisspeptin knockdown in the ARC displayed a significantly reduced number of both regular and complete oestrous cycles and significantly longer cycles over the 100-day period of the study. Further, kisspeptin knockdown in the ARC resulted in a decrease in LH pulse frequency. These data suggest that maintenance of ARC-kisspeptin levels is essential for normal pulsatile LH release and oestrous cyclicity.

Peripheral administration of prokineticin 2 potently reduces food intake and body weight in mice via the brainstem.

BACKGROUND AND PURPOSE: Prokineticin 2 (PK2) has recently been shown to acutely reduce food intake in rodents. We aimed to determine the CNS sites and receptors that mediate the anorectic effects of peripherally administered PK2 and its chronic effects on glucose and energy homeostasis. EXPERIMENTAL APPROACH: We investigated neuronal activation following i.p. administration of PK2 using c-Fos-like immunoreactivity (CFL-IR). The anorectic effect of PK2 was examined in mice with targeted deletion of either prokineticin receptor 1 (PKR1) or prokineticin receptor 2 (PKR2), and in wild-type mice following administration of the PKR1 antagonist, PC1. The effect of IP PK2 administration on glucose homeostasis was investigated. Finally, the effect of long-term administration of PK2 on glucose and energy homeostasis in diet-induced obese (DIO) mice was determined. KEY RESULTS: I.p. PK2 administration significantly increased CFL-IR in the dorsal motor vagal nucleus of the brainstem. The anorectic effect of PK2 was maintained in mice lacking the PKR2 but abolished in mice lacking PKR1 and in wild-type mice pre-treated with PC1. DIO mice treated chronically with PK2 had no changes in glucose levels but significantly reduced food intake and body weight compared to controls. CONCLUSIONS AND IMPLICATIONS: Together, our data suggest that the anorectic effects of peripherally administered PK2 are mediated via the brainstem and this effect requires PKR1 but not PKR2 signalling. Chronic administration of PK2 reduces food intake and body weight in a mouse model of human obesity, suggesting that PKR1-selective agonists have potential to be novel therapeutics for the treatment of obesity.

Alarin stimulates food intake and gonadotrophin release in male rats.

BACKGROUND AND PURPOSE: Alarin is a recently discovered member of the galanin peptide family encoded by a splice variant of galanin-like peptide (GALP) mRNA. Galanin and GALP regulate energy homeostasis and reproduction. We therefore investigated the effects of alarin on food intake and gonadotrophin release. EXPERIMENTAL APPROACH: Alarin was administered into the third cerebral ventricle (i.c.v.) of rats, and food intake or circulating hormone levels were measured. The effect of alarin on the hypothalamo-pituitary-gonadal axis was investigated in vitro using hypothalamic and anterior pituitary explants, and immortalized cell lines. Receptor binding assays were used to determine whether alarin binds to galanin receptors. KEY RESULTS: The i.c.v. administration of alarin (30 nmol) to ad libitum fed male rats significantly increased acute food intake to 500%, and plasma luteinizing hormone (LH) levels to 170% of responses to saline. In vitro, 100 nM alarin stimulated neuropeptide Y (NPY) and gonadotrophin-releasing hormone (GnRH) release from hypothalamic explants from male rats, and 1000 nM alarin increased GnRH release from GT1-7 cells. In vivo, pretreatment with the GnRH receptor antagonist cetrorelix prevented the increase in plasma LH levels observed following i.c.v. alarin administration. Receptor binding studies confirmed alarin did not bind to any known galanin receptor, or compete with radiolabelled galanin for hypothalamic binding sites. CONCLUSIONS AND IMPLICATIONS: These results suggest alarin is a novel orexigenic peptide, and that it increases circulating LH levels via hypothalamic GnRH. Further work is required to identify the receptor(s) mediating the biological effects of alarin.